Arc shield



Jan. 20, 1942. E. WJBOEHNE 2,270,723

ARC SHIELD Filed Aug. 1, 1940 Invent o-r-= Eugen e W. Boehne, FUSION PRODUCTS OF PORTLAND CEMENT-ASBESTOS by W His Attorney.

x W J V the desired shape and size.

Patented 20, 1942 UNITED "STATESpPATENT OFFICE zmoazs ABCBBIELD-I Eugene W. Boehne, Drexel Hill, Pa., assignor to General Electric Company, a corporation of blew York Application amt 1m, No. 349,305 9 Claims. (01. zoo-144i This invention relates to improved (cemented asbestos arc shields or'chute structures co'mmonly used in blow out devices, such as magnetic or gas blast circuit breakers. to confine and extinguish the are drawn between the opening electrical contacts of such devices.

One. type of arc chute to which this invention particularly relates is shown and described in a pe an ereafter allowing the cement to harden m:- the desired form or by machining a block or board of suitable dimensions composed of such hardened cement-asbestos mixtures t The use ofcmenttions for this purpose has a number of advantages Bauding low material cost, ease of manufacture, and ability of the finished shields to resist sudden temperature changes. However. even after flame or other means for producing at least a partial fusion of these surfaces.

For a better understanding of my invention, reference may be had to the accompanying drawing in which Fig. 1 illustrates a partial sectional view of an arcchute embodying my invention similar to the arc chute disclosed in the oo-' pending application referred t above. Fig. 2 is a cross-sectional view taken on line 2-4 of Fig. l, and Fig. 3 is an enlarged view suitably labeled of a portion of Fig. 2 to illustrate'my invention better.

In Fig. '1, I have, illustrated a circuit breaker similar to t at disclosed in the copending application refe red to above comprising an are chute lil associated with which is a pair of relaa Portland cement binder aniesbestg into the desired final tively movable contacts, not shown. Relative movement between these contacts is obtained by means of an operating mechanism generally indicated-at] I. The are chute i0 comprises spaced side walls I! composed of arc-resisting material, each side wall if having on the side facing the other wall a plurality of parallel fins i3 integral with the side walls, which walls It are suitably clamped together by means of members It and bolts I! to form a chutelike structure-perpendicular with the fins extending into the chute opening in staggered interleaved relation with thorough drying, cement-asbestos shields or chutes have not always proven entirely satisfactory in so far as their are interrupting ability has been concerned.

It is, therefore, an object of this invention to provide cement-asbestos chute structures of increased interrupting. capacity capable of interrupting currents of higher values than previous structures of similar type. f

It is a further object to provide an arc shield or'chute with surfaces capable of resisting the eiiects' of high temperature arcs and capable of imparting a greater arc-interrupting capacity to the structure.

According to the present invention the above objects and others, which will .become apparent to those'skilled in the art from the following description of the invention, are attained by subjecting those surfaces of the arc shields or chutes contacted by the arc during the internmtion thereof to a vitrification, for example, by subjecting the surfaces to a suitable intense respect to each other as best shown in Figs. 2 and'3.

. One method by which the invention may be carried into'eflect includes subjecting the chute surfaces to the effects of a hightemperature arc of-brief duration in their assembled position within the breaker structure. Preferably the arc should be of greater intensity than that which the chute will ordinarily encounter in actual use. It is desirable that the duration of this treatment be rather short, preferably of the order of 8 or 10 cycles. In this respect it may be compared with the ordinary power failure arc to which such a chute may be subjected during the opening of a line breaker. However, unless such a circuit were protected by other breakers, the initial operation of the breaker before vitrification occurs would be likely to be accompanied by disastrous results by reason of its failure to protect the line adequately while vitrification still isincomplete.-

Alternatively the surface conditioningof the 'chute may be' accomplished by subjecting the surface to the heat of an arc struck between two spaced electrodes. For example,a high temperature are playing between two electrodes spaced heating agency, such as an electric-arc or. a gas approximately one inch apart may be slowly 2,270,728 passed back and forth over the entire. inner may be started at the center of the chute and the flame worked back and forth along the length of the chute and towards one side until onehalf of the active surface of the chute has been vitrified after which the 'chute is cooled immediately as by immersion. in water for a period of time not exceeding seconds. The remaining half of the chute is then conditioned in the same manner followed by a second cooling in water. I The water treatment used in the flame conditioning process may also be found desirable in connection with the treatment of the shield or chute with an alternating current or direct current are playing between two closely spaced electrodes. As in both of these modifications of the subject process, the heat of the are or the flame has ample time in which to penetrate the shield structure and cause warpage of the chute, periodic cooling is desirable. This effect is not encountered when the conditioning of the chute is carried out with the first method comprising subjecting the chute to an artificial power failure since the treatment in that instance requires only a few seconds as compared with several minutes in either of the other two cases. V

With each of the modifications a somewhat glassy or vitrified surface is obtained on the surfaces of the shield. The appearance of the treated surfaces varies depending upon the type of conditioning treatment used. The intense arc conditioning treatment tends to produce a rather crinkled, cracked or mottled refractory surface containing a number of rather glassy spots thereon whereas the flame conditioned surfaces have a more uniform appearance somewhat resembling ordinary glaze.

Circuit breakers containing arc shields or with untreated chutes which ordinarily failed at about 72,000 kva. on a 2300 volt three-phase line, have consistently cleared 120,000 kva., the

the shield may be first heated in a hydrogen atmosphere at temperatures between 350 and 600 C. for from twenty minutes to four hours and thereafter surface conditioned or conversely the shield may be first surface conditioned and thereafter heat treated in the reducing atmosphere. For practical reasons, the latter sequence has been .found preferable in the manufacture of flame conditioned shields as the hydrogen heat treatment then not only serves to improve the insulation resistance of the shields in accordance with the Arone invention but also serves to dry the chutes which have been immersed in water following the flame conditioning. As the chutes which are are conditioned in a breaker are not subjected to the heat of the are for such a time as to permit actual penetration of the heat into the interior of the chutes, they do not require drastic cooling and may be heat treated in an atmosphere of hydrogen either before or after the arc conditioning as desired.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An arc chute comprising a molded Portland cement-asbestos base, atleast a portion of the surface of said chute being coated with Portland cement-asbestos fusion products.

2. A Portland cement-asbestos arc chute having a partially vitrified surface coating covering at least that portion of the chute surface contacted by the arc during interruption thereof.

3. An arc chute comprising a mixture of Portland cement and asbestos having a refractory coating thereon consisting of the partial vitriflcation product of cement and asbestos.

4.,A Portland cement-asbestos arc chute having a partially glazed surface, said glaze consisting of fusion products of the'chute material.

5. The method of treating a Portland cementasbestos arc chute to improve the arc interrupting properties of the chute which comprises heating at least a portion of the surface of said chute above the fusion point of the cementasbestos mixture.

6. The method of treating a Portland cementasbestos arc chute to improve the arc interrupting properties of the chute which comprises heating at least a portion of the surface of said chute to at least partially vitrify the same.

7. The ineth'od of treating an arc chute comprising a formed'mixture of Portland cement and asbestos to improve the arc-interrupting capacity thereof, which method comprises subjecting capacity of the testing equipment, when equipped with flame conditioned chutes.

Cemented asbestos arc chutes that have been subjected to both the surface conditioning treatment described herein and the reducing atmosphere heat treatment described in the copending application Serial No. 349,010, filed July 31,

1940, in the name of Nicholas P. Arone and 'assigned to the same assignee as the present invention have been found particularly useful in circuit-breaker construction. when subjecting a shield to both treatments, it has been found that at least a portion of the surface of said chute to a high temperature are for a sufficient time to form a fused surface coating on the treated portions of said chute.

8. The method of treating an arc chute comprising a formed mixture of Portland cement and asbestos to improve the arc-interrupting capacity thereof, which method comprises subjecting the surface of said chute to the action of an oxyacetlyene flame until at least a partial fusion of said surface takes place.

9. The process which comprises forming a thin vitrified film on the surface of a cemented asbestos insulating material by means of an oxyacetlyene flame, cooling said material in water, and heat treating said material in a reducing atmosphere consisting substantially of hydrogen at a temperature between 350 and 600 C. for a period of time between twenty minutes and four hours.

EUGENE W. BOEHNE. 

